Field of the Invention
The present invention relates to a linear transmission device, and more particularly to a linear transmission device which can directly detect the change in the distance between the rolling elements.
Related Prior Art
Referring to FIG. 1A, which is a drawing of a linear roller bearing of the related art (U.S. Pat. No. 7,178,981 B2) having a guide carriage 1 which can be mounted on a guide rail 2 in a rolling manner via balls (not shown). The guide carriage 1 is provided with at least one rolling passage (not shown) for the balls, the rolling passage includes a support passage (not shown) for supporting the balls, and a deflecting channel (not shown) that is disposed in the end elements 3 of the guide carriage 1. The balls in the rolling passage are subjected to displacement resistance in the direction of rotation. The end elements 3 are respectively provided with a sensor 4 for detecting the displacement resistance caused by the deformation of the cover plate during the displacement of the balls, so as to determine whether there is abnormality. However, the installation of the above-described sensor 4 generally increases the length of the guide carriage 1, which in turn increases the cost and complexity of the structure, which will affect the travel length.
Please refer to FIG. 1B, which is one of the drawings of the Japanese patent (JP2007225024) showing a ball screw with a sensing device, wherein the sensing device 6 is provided in a recess of a nut 5 (capacitive type, optical type)) for measuring the displacement of the balls 7, and then determining the stress condition of the nut 5. However, the structure of the sensing device 6 changes the size of the nut 5, so that the outer diameter of the nut 5 is increased, which in turn affects the travel length of the nut 5.
Referring then to Japanese Patent No. JP3936519, which discloses a technical content in which a vibration sensor is provided at a bend of an outer circulation member of a ball screw to detect the running condition of the balls, wherein special boring processing has to be performed on the nut to install the vibration sensor, and the boring processing is complicated and the cost is higher. Moreover, installing the vibration sensor at the bend of the outer circulation member, can only detect the stress change caused by the ball striking the wall surface at the bend of the outer circulation member to know the running condition of the balls (for example, insufficient lubrication may cause the ball to run unsmoothly), it is impossible to measure the change in the distance between the balls, and it is impossible to know whether the balls are jammed or not.
The remaining patents, such as Japanese Patent Nos JPA2014159847 and JPA2013200032, all have the above-mentioned disadvantages. Therefore, there is still room for improvement in the conventional linear transmission devices.